The present invention relates to an image forming apparatus applying an electrophotographic process, such as an electrostatic copying apparatus or a laser beam printer. More specifically, the present invention relates to an image forming apparatus provided with a punching function for punching holes to file a paper whereon an image has been formed.
As an apparatus for forming an electrophotostatic lament image on the surface of a copy paper by means of the an electrophotographic process, there have been proposed a variety of types which includes a punching function geared with the operations of the apparatus to automatically punch holes for filing of the paper. In an electrophotographic process, a copy paper is processed by producing an electrostatic latent image formed on the surface of a photosensitive material and by transferring the image to the copy paper, and the image processing is followed by fusing the transferred image by heating and such.
Existing image forming apparatuses having a punching function are roughly divided into two types; one type punches holes in the copy paper in advance of the image processing, and another type punches holes after the image processing and fusing. In the former type, paper crumbs made by punching may adversely affect formation of the image. Accordingly, the latter type apparatus, wherein holes are punched after the image processing and fusing, has become increasingly popular.
The image forming apparatus generally employs a punching means provided with punching cutters movable along a paper delivery passage and with a punching die, for introducing the punching cutters, which is disposed in the delivery passage, opposing the punching cutter. When the punching means punches holes in the paper, the paper needs to be temporarily halted in the paper delivery means. According to the conventional methods of temporarily halting the paper, the leading edge of the paper is adapted to hit a stopper or a discharge roller for carrying the paper out of the apparatus and is temporarily stopped.
However, the apparatus of the above-mentioned composition may cause a crease or fold on the paper, if the paper is halted with the trailing portion thereof caught in a constantly rotating discharge roller which is disposed in a discharge passage. In addition, if the paper is halted with the trailing portion thereof caught in a fusing unit for heating and fusing a transferred image on the paper, the portion caught in the fusing unit may be excessively heated, resulting in a charge in the quality of the paper.
To prevent the creasing and folding of the paper, and changing the quality of the paper with heating, there has been proposed image forming apparatuses, wherein a punching function H for punching holes is disposed near a paper discharge port Y1 in the paper delivery means Y, and a halting portion for halting paper P in a curved condition, as shown by the dot-and-dash line in FIG. 37, is provided between the punching function H and the always constantly rotating delivery roller Y2 (described in JP, A-140755/1983).
The punching function H includes;
a punching means X comprising punching cutters X1 and a punching die X2 having through-holes X2a for receiving the punching cutters;
a stopper H1 for the leading edge of the paper P to hit;
and a discharge roller H2 which stops rotating when the punching means X punches holes. In the punching function H of FIG. 37, a sensor; H3 detects the leading edge of the paper P, extends the stopper H1 as illustrated by the black arrow in FIG. 37, stops the rotation of the discharge roller H2. Cams X3 rotate on a rotary shaft X3a to move the punching cutters X1 up and down.
According to the above mentioned image forming apparatus, if the paper P is so large that the paper P is halted by the stopper H1 and the discharge roller H2 while the trailing portion of the paper is in the delivery roller Y2, the delivery roller Y2 keeps rotating to push forward the trailing portion of the paper P to curve it as illustrated with the dot-and-dash line in FIG. 37. Since the paper P is halted in the halting portion Z in this manner, creasing or folding of on the paper P can be prevented.
For preventing creasing or folding of on the paper halted in the halting portion Z, the paper should be gently curved as shown in FIG. 37. This requires a large space for the halting portion Z in the vertical and in the delivery passage directions. Accordingly it is impossible to miniaturize the image forming apparatus.
When, paper crumbs caught in the punch lock the punching cutter X1 the punching cutter X1 cannot withdraw, and this causes paper to jam therein. Likewise, a paper jam in other parts of the apparatus may stop the image forming apparatus with the punching cutter X1 pushed down by the cam X3. In these situations a jam recovery process should be easily executed in a conventional image forming apparatus having a punching function. To meet this need, there has been proposed an image forming apparatus provided with a punching means X, wherein, as shown in FIG. 38, a punching die X2, also serving as a guide plate for the bottom side of a paper delivery means Y, can be turned downward to open the paper delivery means Y (described in JP-U, A-193698/1988).
The above-mentioned structure, however, requires a space large enough to turn the punching die X2 open for executing jam recovery under the punching means X, and therefore it is difficult to miniaturize the apparatus. Furthermore, the jam recovery operation is difficult, because a user must remove the jam while looking up into the paper delivery means Y, which is far below the eye-level of the user.
In addition, when paper crumbs are caught between the punching cutters X1 and the through-hole X2a in the punching die X2, and it is difficult to open the punching die X2, the jam recovery is more troublesome.
Every image forming apparatus should punch holes at the same position in the paper. But in fact, every apparatus punches holes at any position which may be shifted in the width direction of the paper. The shift stems from, for instance, very close assembly tolerances in manufacturing the image forming apparatus.
As shown in FIG. 39, an image forming apparatus with a punching function normally has a collecting box K to collect paper scraps left after punching holes, the box being disposed beneath the punching die X2 in the punching means X. To remove the paper scraps left after the punching, however, the user must take the trouble to open the main body of the apparatus and to remove the scraps.
To facilitate the removal of the paper scraps, it is suggested to dispose the collecting box K at the upper side of a unit, which turns or moves parallel in one piece, thereby to draw the box out of the main body of the apparatus.
However, in the structure wherein the unit moves to be drawn out, it is not easy to take out the collecting box, because the collecting box K is further under the punching means which is far below the eye-level of the user.
On the other hand, in the structure wherein the box is turned around a shaft disposed under the unit, the collecting box K can be easily taken out because the box is exposed on the upper side of the unit. However, the paper scraps in the box may fall off because the box turns along with turning the unit.
It is normally required to punch two or more holes at regular interval in the width direction of the paper which is carried in the paper delivery means. As shown in FIG. 40 and 41, cams X3 connected to a driving source (not shown) of the image forming apparatus rotate on a rotary shaft X3a, vertically moving a plurality of punching cutters X1 (two cutters shown in FIG. 41). Thus, the cutters punch two or more holes at a time (described in JP, A-260965/1985).
As described above, the punching means X punches two or more holes at a time by using the punching cutters X1, and therefore a great amount of load is applied on the driving source when punching holes. This may affect driving of the other parts of the image forming apparatus. Consequently, if an image forming process is executed on another sheet of paper when the holes are punched, a deviated image may be formed.
When the holes are punched in hard paper such as cardboard in particular, there may occur troubles such as disengagement of a pulley from a timing belt used as a transmission function to transmit the driving force from the driving source to the rotary shaft X3a of cams X3, breakage of the gear used for the transmission function, or bending of the rotary shaft X3a. Hence, it is required to make the transmission function components or the rotary shaft X3a with materials of higher rigidity, or to reinforce the rotary shaft X3a by increasing the thickness thereof. This results in higher production costs or in larger and heavier punching means.